Motor drives and other power conversion systems operate using power from AC power sources, and typically include an input filter to reduce switching noise associated with operation of the power converter, and particularly to control total harmonic distortion (THD) generated by high frequency operation of certain active front end (AFE) rectifiers. In particular, many power conversion systems utilize inductor-capacitor (LC) or inductance-capacitance-inductance (LCL) input filter circuitry associated with each AC input phase to control the harmonic content of a connected power grid. Such filter circuits are subject to damage or degradation of the filter capacitors. Filter capacitor degradation, in turn, may be costly in terms of replacement component costs, labor for inspection and replacement, as well as downtime for the power conversion system and any associated machinery. Thusfar, however, assessing the performance and any degradation in the input filter capacitors has been difficult, and initial capacitor degradation may not be identifiable by visual inspection by service personnel. Certain conventional power converters employ fuses in line with the filter circuit capacitors, but in practice the fuses either do not open quickly enough to prevent capacitor degradation or open frequently in normal operation with healthy capacitors, whereby excessive system downtime results. Accordingly, a need remains for improved filter capacitor degradation prediction or detection apparatus and techniques for use with an active front end power converters.